Time Delay and Integration (TDI) image sensors are commonly used to capture images of moving objects at low light levels in a field of view. TDI image sensors include multiple rows of light sensing elements. Each element accumulates an electric charge proportional to the light intensity at that location in the field of view, and shifts its partial measurement of light incident on the image sensor to an adjacent light sensing element synchronously with the motion of the moving object across the array of light sensing elements.
For example, a first element in a row of elements may receive a charge generated by a first photon generated, or reflected, by a particular point on an object being scanned. The received charge generated by the first photon may be passed from the first element to a second element of the row as the second element also receives a charge generated by a second photon generated, or reflected, by the same point on the object being scanned. Thus, as each element of the row receives a charge generated by a photon generated, or reflected, by the same point on the object being scanned and passes its charge to an adjacent element, the charges generated by the elements in the row accumulate, thereby increasing the low-light imaging capability of the sensor. The total accumulated charge is read out at the end of each row and utilized to generate a digital image.